Process for separating cerium concentrate from ores

ABSTRACT

A process for separating cerium from the other rare earth values in bastnasite ore by roasting the ore followed by leaching with dilute hydrochlorde acid under carefully controlled conditions.

Duncan PROCESS FOR SEPARATING CERIUM CONCENTRATE FROM ORES [75]Inventor: Larry K. Duncan, Chattanooga,

Tenn.

[73] Assignee: W. R. Grace & C0., New York,

[22] Filed: Dec. 29, 1965 [21] Appl. No.: 517,346

[52] US. Cl. 423/21 [51] Int. Cl. C0lg 57/00, C22b 59/00 [58] Field ofSearch 23/15, 19, 23, 87; 423/21 [11 3,812,233 May 21, 1974 [56]References Cited UNITED STATES PATENTS 2,327,992 8/!943 Blumenfeld423/21 Primary Examiner-Herbert T. Carter Attorney, Agent, orFirm-Joseph P. Nigon 57] ABSTRACT A process for separating cerium fromthe other rare earth values in bastnasite ore by roasting the orefollowed by leaching with dilute hydrochlorde acid under carefullycontrolled conditions.

5 Claims, 1 Drawing Figure PATENIEDIAYZI 974 Amt: mE 53 0. v

INVENTOR LARRY K. DUNCAN S W n O? N a d o O I u I? m. 09

, "1 PROCESS FOR SEPARATING CERIUM CONCENTRATE FROM ORES This inventionrelates to the method for the separation of cerium from concentrates ofrare earth carbonate ores. In one particular embodiment, it pertains toa process for the separation of cerium concentrates from bastnasite orethat has been subjected to roasting and certain pretreatment processes.

Bastnasite isan ore that occurs in certain sections of western UnitedStates and contains a relatively large amount of rare earth compounds.The rare earths referred to herein will be understood as those elementshaving atomic numbers 57 to 71 inclusive. The rare earths of mostparticular interest are cerium, europium, lanthanum, praseodymium,neodymium, terbium, gadolinium, and Samarium. I

Bastnasite is a rare earth fluocarbonate which contains traces ofthorium. The mineral is found in deposits in New Mexico, California,Europe and Africa. The crude ore as mined in the California depositcontains a substantial percentage of rare earth oxides. In addition, themineral contains barite, calcite, silicates, aluminates andferromagnesian minerals.

A concentrated bastnasite is commercially available which has thefollowing approximate compositioni Rare Earth Oxides 68 to 70% Fluoride5 to 8% Si0 1.] to L571 CO to This concentrate is the raw material formy novel process. I have found that a cerium concentrate can be preparedin a commercial grade with the concurrent recovery of a similarlyvaluable didymium (mixed rare earth) fraction by controlled acidleaching of the concentrated bastnasite ore. My novel process differsfrom the usual industrial processes in that they normally require totaldissolution of the ore by caustic and/or acid attack. My novel processgives valuable products with a minimum of reaction steps.

In the first step of my process, the bastnasite ore concentrate isroasted at l,000 to 1,500F. This is normally done by the vendor as afinal step in his preparation of the concentrate or it may be done asthe first step of my novel process. The advantage of roasting the I oreis that it drives off additional carbon dioxide and thus concentratesthe ore, the rare earth oxide content increasing to about 90 percent. Inaddition, roasting increases the porosity of the ore and at leastpartially oxidizes the cerium.

In the second step of my process, the ore is leached by mixing the oreconcentrate with dilute hydrochloric acid. The acid concentration mustbe maintained at less than 5 weight percent. Use of a more concentratedacid results in partial dissolution of the cerium and consequently is tobe avoided. Although the acid may be used in concentration as low as 1weight percent, it is obvious that the rate of reaction is improved byoperating at acid concentrations of approximately 3.5 5 weight percent.

The leaching is normally carried out at atmospheric pressure. Althoughsatisfactory results would be obtained in operation at higher pressures,no economic advantage is achieved by such operation and operation atatmospheric pressure is preferred. Although no effort is made toincrease the temperature, the reaction of the hydrochloric acid with theore concentrate is exothermic so there is an initial increase in thetemperature of reaction. This is not objectionable. The reaction can becarried out at temperatures of from 25 to 50C. For obvious economicreasons, operation at room temperature ispreferred.

The leaching is normally carried out in a weight ratio of ore to diluteacid of l :l to about 1:25. The preferred weight ratio is about 1:5 to1:10. The ore is leached for 6 to 24 hours, preferably 12-18 hours.

Both of these products recovered from the bastnasite ore on treatmentwith the process of my invention, have direct commercial applications.The cerium concentrate is recovered as the residue from the process andIhas a purity of about 80 to 90% based on the formu a:

Percent C602 T.O. (Total CeO +rare-earth oxide) Cerium concentrates ofthis purity constitute a commercial grade for uses such as a specialtyglass ingredient or conversion to cerium oxide for glass polishingcompounds. This product may also obviously be used as a raw material forproduction of other and higher pu- EXAMPLE I The feasibility of theleaching of the roasted bastnasite concentrate with a hydrochloricacidwas demonstrated in a run in which 30 grams of the roasted bastnasitepercent minus 325 mesh) was transferred to a standard reaction vesseland leached with a solution of 25 ml. of 12 normal (37 weight percent)hydrochloricacid in 250 ml. of water. The leaching was carried out bystirring the acid with the bastnasite concentrate for a period of 16hours. At the end of this time, the material in the reaction vessel wasfiltered and the filtrate and residues were analyzed. The residuecontained approximately CeO /T.O. An analysis of the didymium (mixedrare earth) chloride solution showed the solution contained less than 2%CeO /T.O.

This run demonstrated the utility of my novel process. The hydrochloricacid concentration was about 4 percent and a cerium concentratecontaining approximately 75 percent was recovered. The solutionrecovered was essentially free of cerium.

EXAMPLE II EXAMPLE Ill In this run, the roasted bastnasite was leachedwith a weight ratio of bastnasite concentrate to hydrochloric acid ofapproximately 1. The leaching was carried out using the techniquesdescribed in Example I. A total of 300 grams of roasted bastnasite wasadded to and leached with a solution containing 250 ml. of 37 weightpercent HCl and 2500 ml. water (concentration approximately 4 weightpercent). The leaching was carried out for a period of 22 hours at roomtemperature. At the end of this time, the slurry was filtered and thefilter cake and the filtrate were analyzed. The filtrate was found tohave a cerium purity of 90 percent and the rare earth chloride solutioncontained only 4.8 percent cerium (CeO /T.O.).

This run demonstrates optimum conditions when a bastnasite ore that hasnot been subjected to the size reduction is used. The purity of thecerium concentrate was high and the didymium chloride solution did notcontain an excessive amount of cerium. I This run also indicated theeffect of leaching time on the efficiency of the separation. Successiveanalyses of soluble and insoluble values, during the course of theleaching indicated the relative rate of solubilization of rare earth vs.cerium values:

Under the conditions of this test, with relatively initial high acidconcentration, some cerium was dissolved in the first 2 hrs. As rareearth extraction proceeded, and the acidity decreased, most of thiscerium reprecipitated into the residue to yield, after dissolution ofmost of the rare earths, a final rare earth chloride with acceptably lowcerium content. Incremental addition of the total acid over the leachingperiod minimizes this slight initial dissolution of cerium.

The drawing is a graphical presentation of the above data and provides ageneral indication of the optimum leach time, under these conditions oftemperature, initial acid concentration, and ore/acid ratio.

EXAMPLE IV The effect of the particle size of the bastnasite ore wasinvestigated in a series of runs in which the bastna-v site oreconcentrate was reduced in size to about 5 microns or less and leachedusing the techniques described in Example I. In the first of theseseries of runs,

150 grams of this finely divided roasted bastnasitecon; centrate wasleached with a solution of 1250 ml. of water containing 125 ml. ofhydrochloric acid (approximately 4 weight percent concentration). Theleaching was carried out for a period of about 20 hours. At the end ofthis time, the products were separated as described above and the rareearth chloride solution analyzed for cerium. The solution was found tocontain 5% CeO EXAMPLE V An effort was made to determine the best ratioof fine sized bastnasite to acid. In this run, grams of.

roasted bastnasite concentrate that had been reduced to a size of about5 microns and leached with asolytion of 1250 ml. of water containing ml.of hydrochloric acid. This represents a 50 percent increase, relative toExample IV, in acid/ore ratio. The leaching was carried out for a periodof 20 hours. At the end of this time, the slurry was filtered and theresidues and filtrate analyzed. The residue was found to have a CeOpurity of about 87 percent. The rare earth chloride solution, however,contained 12.5% CeO /T.O.

EXAMPLE VI The effect of acid concentration was investigated in thisrun. A total of grams of the bastnasite concen- -tratethat had beenreduced to 5 micron size was EXAMPLE VII In this example, the effect ofthe ratio of ore to acid solution was investigated further. The ore feedwas roasted at l400-1500F., and sized to nominally less than 10 microns.A total of 300 grams of this fine-sized bastnasite was added to andleached with a solution of 250 ml. of hydrochloric acid in 2,500 ml. ofwater (acid concentration approximately 4 percent). The reaction wascarried out for a period of about 20 hours. At the end of this time, theslurry was filtered and the filter cake and solubilized materialsanalyzed. The cerium concentrate was found to have a Ce0 purity of 88percent. The rare earth chloride solution contained 7% CeO /T.O.

It is apparent from a review of the data presented in Examples IV to VIIthat advantages are achieved by reducing the size of the roastedbastnasite concentrate prior to the acid leach. When the material wasreduced 'in size to below 5 microns and the acid solution kept inexcessive? only to the extent that it would decrease the immediate valueof the didymium chloride fraction. if the cerium concentrate is theprimary product desired, or if the didymium fraction is to be usedprimarily for feed to other purification operations in which low (i.e.,less than -15 percent) cerium content is of minor importance, or if thefinal leach slurry is to be given a terminal treatment forreprecipitation of soluble cerium, it is obvious that minimizing thedissolution of cerium during leaching would be less important.

Obviously many modifications and variations of the invention may be madewithout departing from the essence of the scope thereof and only suchlimitations should be a part of the appended claims.

What is claimed is: 1. A process for preparing a cerium concentrate anda non-cerium rare earth chloride solution from a bastnasite oreconcentrate which comprises the steps of:

a. Roasting the ore concentrate at a temperature of about l000 to 1500Ffor about 1 to 4 hours to drive off a substantial portion of the carbondioxide, b'. Leaching the roasted ore concentrate with an about 1 to 5percent hydrochloric acid solution for 6 to 24 hours, c. Filtering andrecovering the cerium concentrate andthe non-cerium rare earth chloridesolution.

2. The process according to claim 1 wherein the weight ratio of roastedbastnasite ore to hydrochloric acid used in the leaching is from 1 to lto l to 10.

3. The process according to claim 1 wherein the roasted ore is reducedto a size of about 5-10 microns prior to leaching.

4. The process according to claim 1 wherein the leaching is carried outat about 25 to 50C. and atmospheric pressure.

5. A process for separating cerium values from noncerium rare earthvalues from a bastnasite ore concentrate which comprises:

a. Roasting the ore concentrate at a temperature of about l,000 tol500F. for a time sufficient to drive off a substantial portion of thecarbon dioxide whereby cerium values are selectively converted to a formsubstantially insoluble in aqueous acid leach solution and non-ceriumrare earth values are converted to a form soluble in said leachsolution,

' b. Leaching the roasted ore concentrate with an about 1 to 5 weightpercent hydrochloric acid solution for a time sufficient to solubilizenon-cerium rare earth values, and,

c. Separating the leach solution containing noncerium rare earth valuesfrom the undissolved concentrate containing cerium values.

2. The process according to claim 1 wherein the weight ratio of roastedbastnasite ore to hydrochloric acid used in the leaching is from 1 to 1to 1 to
 10. 3. The process according to claim 1 wherein the roasted oreis reduced to a size of about 5-10 microns prior to leaching.
 4. Theprocess according to claim 1 wherein the leaching is carried out atabout 25* to 50*C. and atmospheric pressure.
 5. A process for separatingcerium values from non-cerium rare earth values from a bastnasite oreconcentrate which comprises: a. Roasting the ore concentrate at atemperature of about 1, 000* to 1500*F. for a time sufFicient to driveoff a substantial portion of the carbon dioxide whereby cerium valuesare selectively converted to a form substantially insoluble in aqueousacid leach solution and non-cerium rare earth values are converted to aform soluble in said leach solution, b. Leaching the roasted oreconcentrate with an about 1 to 5 weight percent hydrochloric acidsolution for a time sufficient to solubilize non-cerium rare earthvalues, and, c. Separating the leach solution containing non-cerium rareearth values from the undissolved concentrate containing cerium values.